Hydrogen sensors are well known in the industry. The current sensors have very long response times and have high cross-sensitivity for other gases due to the use of detector electrodes comprised of semiconductor oxides.
A growing need in the industry is the ability to manufacture fast-acting, accurate hydrogen sensors to detect hydrogen gas with the lowest possible cross-sensitivity for other gases. Accordingly, the need exists for a conductor composition with the greatest hydrogen permeability.
The solubility of hydrogen in palladium has been well known to scientists. Its use as a probe for measuring hydrogen content, however, is a recent adaptation. Previous attempts to prepare hydrogen sensors using palladium deposited by thin film techniques proved less than satisfactory due to the film being extremely thin, causing high resistivity and the film being nonporous causing relatively slow hydrogen diffusion through the film, resulting in slow response time.
Palladium thick film compositions have typically been used as capacitor electrodes but not for detector electrode applications. In order to maximize conductivity of the compositions in an extremely thin metallization application, pure palladium conductors are typically fired over 1100.degree. C. This firing range is not desirable for producing detector electrodes, therefor, those skilled in the art have thought it to be necessary to add silver to the thick film compositions. The addition of silver causes the Pd/Ag metallization to have low porosity resulting in slow hydrogen diffusion and reduced hydrogen solubility. The present invention answers this need by offering a palladium thick film conductor composition suitable for use in a hydrogen sensor.